Gas turbines are finding increasing numbers of applications and uses in modern technology and are expected in the next decade to become the most economical and flexible method of energy production from carbon and hydrogen containing fuels.
Gas turbines have been found to be particularly advantageous in the developing energy system referred to as cogeneration and which involves the joint generation of electric current and steam, where such gas turbines have significant advantages.
Gas turbines for use in energy generating applications and in many other cases may consist of a compressor and a turbine which have a common shaft or are so interconnected that the apparatus can operate in accordance with the Joule cycle, i.e. at constant pressure. Air is compressed in the compressor and is fed to a combustion chamber in which the temperature of the gases is increased while the pressure remains constant. The hot gases then drive the turbine.
It is known that the compressors of such gas turbines become soiled and coated with deposits which reduce the operating efficiency. Accordingly, such compressors must be cleaned continuously or repeatedly whether during a standstill of the gas turbine or, more advantageously, during its operation, i.e. by a so-called "on-line" cleaning system. This latter type of cleaning is usually accomplished apart from the traditional scrubbing of such turbines while they are out of operation, at reduced rotational speeds. The advantage of the on-line cleaning is that the compressor efficiency can be maintained or improved without the need to bring the apparatus to standstill and without cooling down of the apparatus. Since downtime can be avoided, the overall output of the apparatus can be improved.
Basically such on-line cleaning should be carried out frequently especially at certain time intervals. A complete replacement of the conventional off-line scrubbing or conventional dry cleaning of the turbine during an interruption in operation, is not the prime intention. However, the on-line cleaning allows fewer off-line cleaning cycles to be used and hence fewer interruptions in the operation of the apparatus in which also dry cleaning agents, such as ground nut shells, hard rice, synthetic resin particles or the like are employed and may, because of their abrasive characteristics, give rise to deterioration of the compressor blades and their coatings.
Up to now, on-line scrubbing mainly uses demineralized water, for example condensate water, having a total content of solids to a maximum of 5 ppm and containing the metals (Na+K+Pb+V) to a maximum of 0.5 ppm.
With respect to the on-line cleaning it is to be noted that the deposits which may arise on the compressor blades can accumulate in the hot regions in the turbine and can there have detrimental effects. It is necessary, as a consequence, depending upon the fields of application, operating conditions and the like to carefully monitor such on-line scrubbing operations.
With on-line as well as traditional off-line scrubbing it is important to achieve the highest possible degree of removal of all deposits and cleaning of the blades. The more complete the removal of such contaminants the better will be the operating efficiency of the apparatus and the less the frequency with which abrasive dry cleaning must be carried out to the point that such abrasive cleaning can be rendered totally superfluous.